1. Dept. of Electrical and Electronics Engineering, Univ. of the Ryukyus, Okinawa 903-0213, Japan
2. Dept. of Computer Sciences and Electronics, Kyushu Institute of Technology, Iizuka, Fukuoka 820-8502, Japan
3. Center for Interdisciplinary Research, Tohoku Univ., Aoba-ku, Sendai 980-8578, Japan
4. Dept. of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8535, Japan